This disclosure generally relates to systems and methods for the protection of imaging devices against light having a high radiant flux. As used herein, the term “high-radiant-flux light” means light having any one or more of the following measurable properties: high radial intensity (W/sr), high irradiance (W/m2) and high radiance (W·sr−1·m−2). Such high-radiant-flux light may be coherent (e.g., laser light) or incoherent.
A general problem is to achieve high probability of mission success, at acceptably low cost, despite hazards. A hazard of increasing concern is high-radiant-flux light, which can damage optical sensors (hereinafter “image sensors”) needed to (a) operate a vehicle safely or (b) collect data, such as agricultural data or military surveillance data. This hazard usually arises from lasers aimed at a vehicle. However, it may also arise from arc welding equipment, exceptionally large or hot fires, a lightning bolt, or a nuclear blast.
Imaging devices, such as cameras and telescopes, are especially vulnerable to high-radiant-flux light. By design, such imaging devices use a lens or mirror to focus light onto an image sensor (such as a focal plane array) comprising a multiplicity of pixels. This greatly increases the light intensity on pixels corresponding to the location of the high-radiant-flux light source in the image. Thus, light that is harmless to a structural surface may have damaging radiant flux at the image sensor. The high-radiant-flux light can damage the image sensor by thermal shock, melting, or other mechanisms.
One approach to solving this problem is using a laser sensor to detect the presence of high-radiant-flux light in the imaging device's field of view. As used herein, the term “laser sensor” means a sensor that detects high-radiant flux light (defined above). (For avoidance of doubt, it should be noted that the term “laser sensor” as used herein does not mean a sensor that detects laser light only or a sensor that detects all laser light. Instead the laser sensor detects any light having a radiant flux in excess of a specified threshold, including but not limited to high-radiant-flux laser light.) The laser sensor transmits a signal via a signal line to a shutter inside the imaging device. The shutter closes, blocking the light from reaching the image sensor of the imaging device. This approach suffices for the weakest threats, such as accidental exposure to lasers used in a light show, but it is insufficient for the more intense light commonly encountered in military situations due to reaction time delays in such a system.
It would be advantageous to equip imaging devices with protection systems that can block even the highest-intensity light before it damages the image sensor.